The most interesting of our Interaction Device developments may well be this simple ring like IR device that enables direct pointing.  By direct pointing we mean that the device continually returns the position in a plane (normally a display screen)  that your finger is pointing at - the most natural  pointing technique we can think of.
The device is described in US Patent # 6,184,863.  A more reader friendly description is in our UIST97 paper .

If you want to see the device in action, you can look at this (6.7mb) Quicktime video or the higher resolution (12mb) version. You may need to update your Quicktime plug-in.